Figure 1.

Method used for macroscopic impedance measurements and numerical simulations in different preparations. (A) Scheme of the experimental setup. Left: Two borosilicate micropipettes with silver-chloride electrodes and a ground electrode are placed in the ACSF solution. One electrode is used in whole-cell configuration to send white-noise current and simultaneously measure the voltage response of the recorded neuron (acquisition sampling rate: 50 kHz); the other electrode used as a reference is located 5 to 10 μm away from the recorded neuron. Middle: Frozen Gaussian white noise (amplitude: ± 5 to 20 pA; duration: 20 s) is injected repeatedly into patched neurons. Right: Fourier modulus of the injected current as a function of frequency confirms that each frequency from 0 to 10,000 Hz is uniformly sampled. (B) Equivalent electrical circuit between intracellular and extracellular electrodes. (C) Equivalent electrical circuit between the extracellular electrode and the ground. Z_a is the impedance of the region defined by the isopotential surface ${\mathcal{S}}_1$ passing through the extracellular electrode and the first isopotential surface ${\mathcal{S}}_g$ that totally includes the neuron, $Z_s$ is the impedance of the part of the soma included between ${\mathcal{S}}_1$ and ${\mathcal{S}}_g$, Z_d is the input impedance of the dendrite between surfaces ${\mathcal{S}}_1$, ${\mathcal{S}}_g$, and Z_g is the impedance of the region between ${\mathcal{S}}_g$ and the ground. $Z_g=\left(Z_a\left|\left|Z_s\right|\right|Z_d\right)\oplus R_g$ where $\parallel$ means “in parallel” and $\oplus$ “in series.” To see this figure in color, go online.